1. Multi-beaming & Wide Field Surveys
Anne Green
University of Sydney
15 May, 2003
Multibeaming & Wide Field Surveys

2. Multibeaming definitions Molonglo Observatory Synthesis Telescope
Outline
Multibeaming definitions
Molonglo Observatory Synthesis Telescope
The SKAMP Project
SKA & Multiple possibilities
15 May, 2003

3. Multibeaming principles and definitions
Everyone is doing it!
Let’s get the terms right
Primary beam – individual element
Fields of view & multiple beams
15 May, 2003

4. Observing teams with their own beams
Multi beams
Station beams
Element antenna pattern = primary beam
Synthesized beams from correlator 16 12
Observing teams with their own beams
Can have all beams simultaneously 8 4
15 May, 2003

5. Molonglo Observatory Synthesis Telescope
Photo: G. Warr
15 May, 2003

6. Current Observing Statistics
843 MHz continuum
3 MHz bandwidth
43” spatial resolution
Field of view 23’ – 160’
Number of beams formed
Sensitivity ~1 mJy/beam
Dynamic range ~200:1
Full synthesis in 12 hr
15 May, 2003

7. 15 May, 2003

8. Rotation of fan beams during an observation
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9. A wider field of view with minimum grating artefacts
15 May, 2003

10. Instantaneous versus synthesis visibility functions & beamshapes
15 May, 2003

11. Continuous uv coverage gives excellent image quality:
1.6 km
(Bock et al. 1999)
Continuous uv coverage from 15 m to 1.6 km in 12hr synthesis
15 May, 2003

12. Faxplot and image for Field 2144 (J0127-366)
15 May, 2003

13. Faxplot and image for Field 971 (J2018-557)
15 May, 2003

14. Real time beam-forming at Molonglo
15 May, 2003

15. Coverage with small Field of View (1982 – 1997)
15 May, 2003

16. SUMSS Survey Fields d < -30 degrees (1997 – 2003)
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17. Molonglo Galactic Plane Survey image at 843 MHz
15 May, 2003

18. The Square Kilometre Array Molonglo Prototype (SKAMP)
Goal: To equip the Molonglo telescope with new feeds, low-noise amplifiers, digital filterbank and FX correlator with the joint aims of:
developing and testing SKA-relevant technologies and
providing a new capability for low-frequency radio astronomy in Australia
15 May, 2003

19. Key features of SKAMP
Collecting area = 1% of SKA (i.e. equivalent to 1 SKA station)
Multibeaming
Wide instantaneous field of view
Digital beamforming
Wide-band FX correlator (2048 channels)
Frequency and pointing agility
Wide-band line feeds and LNAs
Cylindrical antenna prototype
Adaptive null steering and adaptive noise cancellation
- Photonics for LO distribution, signal gathering and beam forming.
- Resurface telescope to operate at higher frequency
- ‘Software telescope’ - computerised control, beam forming and data acquisition
- Automated remote operation, data pipeline
- New low-noise amplifiers
Result: MHz radio ‘spectrometer’ with >5 times increase in continuum
sensitivity, high dynamic range, fully-sampled uv plane.
15 May, 2003

20. Target specifications
Parameter
1420 MHz
300 MHz
Frequency Coverage
300–1420 MHz
Bandwidth (BW)
250 MHz
Resolution (δ < -30°)
26" x 26" csc|δ|
123" x 123" csc|δ|
Imaging field of view
1.5° x 1.5° csc|δ|
7.7° x 7.7° csc|δ|
UV coverage
Fully sampled
Tsys
< 50K
< 150K
System noise (1σ) 12 hr: 8 min:
11 μJy/beam 100 μJy/beam
33 μJy/beam 300 μJy/beam
Polarisation
Dual Linear
Correlator
I and Q (Full Stokes at 125 MHz BW)
Frequency resolution
120–1 kHz (FXF mode: 240 Hz)
Independent fanbeam
1.3’ x 1.5°
6.2’ x 7.7°
Indep. fanbeam offset
±6°
±27°
Sky accessible in < 1 s
180 deg2
1000 deg2
15 May, 2003

21. Signal Path and Antenna Pattern
Cylindrical Parabolic Collectors
(Two collinear 778 m x 12 m)
MHz Feed and LNA
(7,400 feeds, 14,800 LNAs)
Delay line beamforming
Analog to Digital Converter
(1,600 8 bit 250 MHz BW ADCs)
Digital delay beamforming
(80 x10 m x 10 m patches)
Digital filterbank (160)
(Two 250 MHz/patch)
FX Correlator
(3,160 baselines, 2,048 channels)
Signal processing & storage
(imaging, spectrometer, searching...)
Independent fanbeam
Digital Beamformer
(64 fanbeams within imaging beam)
[Requires extra funding]
Single feed beam
Delay line beam
Independent fanbeam
Imaging beam
15 May, 2003

22. Science outcomes & goals
Imaging survey at range of frequencies
High redshift HI absorption in galaxies
Transient source monitoring
Pulsar survey
Radio recombination lines & absorption observations of HII regions
SNR searches – ISM structure
15 May, 2003

23. Science goals: High-redshift radio galaxies using continuum data
Radio spectral index measurements using MOST and other catalogues below about 1400 MHz are an efficient way of selecting high-redshift (z>3) radio galaxies (e.g. de Breuck et al. 2000).
Radio galaxy TN at z=5.19 (van Breugel et al. 1999)
15 May, 2003

24. Science goals: HI absorption spectra from distant galaxies
(Lane 2000)
MHz range and 2048 spectral channel FX correlator enables:
Measurements of HI absorption at z ~ 0.75 that capitalise on the large collecting area of MOST
Stage II enables ΩHI measurements at z ~ 0.75, where other methods are not well constrained
15 May, 2003
(Lane and Briggs 2001)

25. RFI at Molonglo 200-1500 MHz (Measured 25 June 2001)
UHF TV
VHF TV
GSM
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26. The Square Kilometre Array (SKA) Project
Multiple beams & multiple FOV
Benefits of baseband recording
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27. Multibeaming with the SKA
Primary beam – individual element
Field of view – continuous image area
* whole SKA or sub-array
* single station (or core)
Multiple beams – within FOV
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28. SKA Poster
15 May, 2003

29. Large, imaging Fields of View
Contiguous FOVs: blind survey over large area, continuous Galactic structures
HI in emission and the Cosmic web
Formation & evolution of galaxies: clustering, lensing
Separated FOVs: parallel projects, deep survey
15 May, 2003

30. Multiple beams – in one FOV
Pulsar timing
Multiple targets – X-ray binaries (XRBs), g-ray bursters (GRBs), supernovae (SNe)
Simultaneous, multi-frequency studies of intra-day variables (IDVs)
RFI mitigation
15 May, 2003

31. Expensive on computer time.
Baseband recording
By the Nyquist theorem, we can store all the information by sampling at twice the bandwidth and saving the data to tape.
Expensive on computer time.
Hold up to 1 hour data in buffer – save when triggered, limited to one FOV.
Targets – GRBs, pulsar glitches & timing, SNe, polarisation, RFI mitigation.
15 May, 2003

32. Practical Demonstration of reciprocity
Molonglo Observatory Synthesis Telescope
Light Emitting Analogue of Synthesis Telescope
15 May, 2003